As is generally well known, users of material destruction devices such as grinders, shredders and hammer mills, or material destruction services employing such devices must consider equipment throughput capability as it directly affects the material destruction costs. A direct relationship between equipment throughput and material destruction costs exists, wherein the higher throughput, measured in pounds per hour, results in lower costs of material destruction.
However, the throughput is adversely affected by the cut or final particle size of destructed material wherein the smaller particle size results in decreased throughput. Lately, smaller particle size is required in destructing materials containing sensitive information, for example, computer disks and/or credit cards, due to increased security concerns and data theft. The cut particle size is determined by the size of openings formed within screens used on such devices and, more particularly, on grinders and hammer mills. Reduction of the screen opening sizes results in a reduced cut particle size.
Accordingly, customers of sensitive information have been willing to absorb higher costs of destructing the material containing such sensitive information. Oppositely, customers of non-sensitive materials which are to be simply recycled require larger opening sizes in order to increase throughput and reduce material destruction costs. Prior to the present invention, the screens presently in widespread use have openings of a fixed size requiring screen changeout to provide a different opening size and, even more particularly, to provide a different particle size.
The particle size is particularly important to operators of mobile destruction services that employ trucks containing material destruction devices who must change the screen depending on specific customer requirements. The effort to change the screen is complicated by the fact that the screen on such mobile trucks is located between the devices and the payload storage compartment of such truck. Specifically, in applications involving security material grinders, the fasteners holding the screen to the frame of such material grinder must be first removed from each side of the truck. Next, the protective screen cover is removed from the inside of the payload compartment and then the screen itself is removed from the material grinder. A reverse procedure is used to install the screen having openings of the desired size. Accordingly, the effort required to change the screen increases the downtime and further increases the material destruction costs.
Efforts have been made to reduce the need for replacing screens by providing an adjustable dual screen device consisting of a fixed and a movable screen member wherein the movable screen is manually adjusted to very the opening size. U.S. Pat. No. 2,954,175 issued to Humhrey et al, U.S. Pat. No. 2,315,651 issued to Peterson, U.S. Pat. No. 2,661,159 issued to Thomas, U.S. Pat. No. 2,440,927 issued to Boss et al; U.S. Pat. No. 2,520,718 issued to Hanson, U.S. Pat. No. 1,847,193 issued to Peters, U.S. Pat. No. 1,523,614 issued to Shelton U.S. Pat. No. 121,192 issued to Page and U.S. Pat. No. 1,133,421 issued to Terway disclose various manually adjustable dual screen devices.
However, the prior art type adjustable dual screen devices still require greater than desired effort to adjust the opening size and, therefore, have failed to gain wide acceptance in the material destruction industry and particularly in the mobile destruction services industry.